1. Field of the Invention
The invention relates to the production of ceramic composite materials comprising a fibrous structure embedded in a matrix, and more particularly a structure of silicon carbide fibers in a matrix of ceramic.
2. Description of the Prior Art
Liquid precursor infiltration and pyrolysis can be used for processing ceramics and their composites. See S. J. Glass and D. J. Green, "Surface Modification of Ceramics by Partial Infiltration," Adv. Ceramic Mater., 2, 2, 129-131 (1987); B. R. Marple and D. J. Green, "Incorporation of Mullite as a Second Phase into Alumina by an Infiltration Technique," J. Am. Ceram. Soc., 7111!C-471-C-473 (1988); M. D. Sacks and S. D. Vora, "Preparation of SiO.sub.2 Glass from Model Powder Compacts: III, Enhanced Densification by Sol Infiltration," J. Am. Ceram. Soc., 71 4!245-49 (1988); B. E. Walker, Jr., R. W. Rice, P. F. Becker, B. A. Bender, and W. S. Coblenz, "Preparation and Properties of Monolithic and Composite Ceramics Produced by Polymer Pyrolysis," Am. Ceram. Soc. Bull., Vol. 62, No. 8, 916-23 (1983); W. C. Tu and F. F. Lange, "Liquid Precursor Infiltration and Pyrolysis of Powder Compacts, I: Kinetic Studies and Microstructure Development," sent to J. Am. Ceram. Soc; W. C. Tu and F. F. Lange, "Liquid Precursor Infiltration and Pyrolysis of Powder Compacts, II: Fracture Toughness and Strength," sent to J. Am. Ceram. Soc.; and W. C. Tu, F. F. Lange and A. G. Evans, "A Novel, Damage-Tolerant Ceramic Composite (Synthetic, High-Temperature Wood)," sent to J. Am. Ceram. Soc.
The precursor is a liquid, comprising metal organic molecules dissolved in an appropriate solvent. The excess solvent is removed by evaporation and the solid precursor molecules are decomposed (pyrolyized) into the desired inorganic with a heat treatment. A powder compact can be infiltrated with a liquid precursor and pyrolyzed to synthesize an inorganic phase within the porous, ceramic. See S. J. Glass and D. J. Green, supra; B. R. Marple and D. J. Green, supra; M. D. Sacks and S. D. Vora, supra; B. E. Walker, Jr., R. W. Rice, P. F. Becker, B. A. Bender, and W. S. Coblenz, supra; and W. C. Tu and F. F. Lange, "Liquid Precursor Infiltration and Pyrolysis of Powder Compacts, I: Kinetic Studies and Microstructure Development," sent to J. Am. Ceram. Soc.
A variety of unique microstructures (graded, multi-phase, partially porous to fully dense, etc.), having unique thermomechanical properties can be fabricated. In addition, the pyrolyized precursor can be used to both increase the relative density and strengthen the powder compact without shrinkage. See, W. C. Tu and F. F. Lange, "Liquid Precursor Infiltration and Pyrolysis of Powder Compacts, I: Kinetic Studies and Microstructure Development," sent to J. Am. Ceram. Soc.
The lack of powder shrinkage during strengthening is an advantage for ceramic composites. Conventional strengthening by densification is constrained by the fibers and leads to the formation of crack-like voids. See, O. Sudre and F. F. Lange, "Effect of Inclusions on Densification: I, Microstructural Development in an Al.sub.2 O.sub.3 Matrix Containing a High Volume Fraction of ZrO.sub.2 Inclusions," J. Am. Ceram. Soc., 753!519-24 (1992).